TOEICの学習に限らず、英語を学ぶのであれば英和辞典は必携の書の一つでしょう。

、。

Not just for TOEIC study — if you're learning English at all, an English-Japanese dictionary is one of the essential books to have.

Literal

TOEIC [possessive-の] study [to-に] not-limited-to, English [object-を] learn [if-のであれば] English-Japanese dictionary [topic-は] essential book [possessive-の] one [probably-でしょう].

~に限らず 'not limited to' broadens the scope from TOEIC to all English study. 必携の書 'essential book to carry' — 必携 'must-carry' is a formal compound. のであれば is a formal conditional: 'if it is the case that.' A recommendation with a textbook-like authority.